Topological insulator array serves as reconfigurable photon router

Since their discovery in 2005 by two physicists at the University of Pennsylvania (Philadelphia, PA), topological insulators—materials and devices that route carriers (such as electrons and photons) freely along their edges without dissipation or backscattering, while being insulating in their interiors—have paved the way towards efficient circuits for computations. However, the routes available in these devices have up to now been restricted to along the predefined path of their static physical boundaries, wasting the interior space. Now, a new topological insulator design from a new generation of researchers at the University of Pennsylvania has been created to route photons within the entire footprint of the device. 

Essentially functioning as an “optical” topological insulator, the photon router is fabricated as an array of tessellated oval rings comprised of indium gallium arsenide phosphide (InGaAsP) racetracks approximately 500 nm wide and with maximum/minimum dimensions for the oval of around 18 µm/12 µm fabricated on an indium phosphide (InP) wafer and further transferred to a glass substrate. By dynamically illuminating a sub-area of rings in the array with a 1064 nm nanosecond pulsed pump laser, photons in the telecommunications band at around 1500 nm can travel from one ring to the other along the boundary of the pumping area in an unlimited fashion, creating a reconfigurable yet ultracompact photonic router. Designed for telecommunications wavelengths, the router would be ideal for photonic integrated circuits if the external pumping controller for the rings could be miniaturized or integrated with the array to enable practical applications in commercial optical datacenters. Reference: H. Zhao et al., Science, 365, 6458, 1163–1166 (Sep. 13, 2019).